Arthroscopic reconstruction of anterior cruciate ligaments with allograft: single-tunnel single-bundle versus single-tunnel double-bundle techniques

Inclusion and exclusion criteria

The inclusion criteria were: (1) patients had subjective instability, and abnormal knee laxities were confirmed by the Lachman test and pivot shift test; (2) ACL rupture was confirmed by magnetic resonance imaging (MRI); (3) 18 years of age or over; (4) unilateral primary ACL injury; (5) patients had no or minimal osteochondral degeneration on radiographic examination; (6) patients underwent arthroscopic STDB or STSB ACL reconstruction with anterior tibialis tendon allografts.

The exclusion criteria were: (1) damage to multiple ligaments or injury of the articular cartilage; (2) radiographic evidence of Kellgren–Lawrence grade 3 or 4 osteoarthritis (OA) and/or severe osteoporosis; (3) bilateral ACL injuries; (4) partial ACL rupture; (5) concomitant total or subtotal meniscectomy; (6) young patients with unclosed growth plates.

Patient information

This retrospective study was carried out upon receiving approval from our institution’s ethical review board. Overall, 78 patients who visited our department from March 2012 to June 2013 met our inclusion criteria and were recruited for this study. The duration from injury to surgery ranged from 3 days to 12 months. There were 60 patients with a meniscus injury, for whom the menisci were sutured, shaped, or resected according to the type of injury. All of the surgeries were performed by the same senior surgeon, with either STSB reconstruction (N  = 36) or STDB reconstruction (N = 42) performed, which was randomized with closed envelopes. A flowchart of the patient selection process is presented in Fig. 1.

Fig. 1figure 1

Flow diagram of the study design

Allograft preparation

The anterior tibialis tendon allografts (Bone Tissue Engineering Library, Shanxi, China) were prepared on a back table after thawing in 37 °C normal saline. The length of the tendon (24–30 cm) was measured and doubled on itself; then the ends of the tendon were whip-stitched for about 35 mm with No. 2 Fiberwire suture (Arthrex). In the STSB group, the allograft was folded and weaved into a single bundle with a length of over 7 cm and a diameter of 8–9 mm. In the STDB group, the allografts were separated into AM and PL bundles. The AM bundle was over 6.5 cm in length and 6–7 mm in diameter, while the PL bundle was over 5.5 cm in length and 5–6 mm in diameter. Then the graft was clamped at either end on the preparation board with 10 lb of tension. The tendon allograft was kept moist until implantation.

Anesthesia and exposure

The surgeries were performed on patients in a supine position, with the affected knee flexing at an angle of 90° to allow the lower leg to naturally droop beside the bed. Epidural anesthesia was administered. A tourniquet was applied around the upper thigh. A routine external anterior approach under arthroscopy was performed in order to confirm the diagnosis of a torn ACL.

STSB ACL reconstruction

The knee was examined by arthroscopy following conventional procedures to confirm the diagnosis (Fig. 2A). In accordance with our previous publication [2], both the lateral intercondylar ridge and the lateral bifurcate ridge were important bony landmarks for the femoral attachments of the ACL. The femoral tunnel, which should not surpass the lateral intercondylar ridge, was created in the center of the lateral bifurcate ridge. A K-wire was placed into the lateral femoral condyle at the 1:30 or 10:30 position through the AM portal using a freehand technique at 120° of knee flexion (Fig. 2B). Using the inserted K-wire as the reference, a femoral tunnel was reamed to the lateral cortex of the distal femur using a 4.5 mm EndoButton drill. A 30 mm femoral socket that matched the prepared graft diameter was then created using a cannulated reamer. The tibial tunnel was placed at the center of the ACL remnant through the AM surface of the tibia at the level of the tibial tubercle using a tibial guide (Smith & Nephew Acufex) (Fig. 2C). The graft was first introduced into the tibial tunnel with a guide wire and then pulled directly into the femoral tunnel and fixed on the femoral side by flipping over the EndoButton (Smith & Nephew) (Fig. 2D, E). The tibial side was fixed using a hydroxyapatite interference screw (DePuy Mitek) with a diameter 1 mm larger than the graft at 3° of knee flexion under 40 N of initial tension.

Fig. 2figure 2

Surgical procedures for STSB ACL reconstruction under arthroscopy. A Diagnosis of ACL rupture under arthroscopy. B Femoral tunnel. C Tibial tunnel. D Graft was pulled into the femoral tunnel. E Reconstructed ACL

STDB ACL reconstruction

After confirming the ACL rupture (Fig. 3A), both the femoral and tibial tunnels were created using a method similar to the STSB technique (Fig. 3B, C). The AM and PL bundles were looped over a single strand of suture, and a graft-positioning tool was used to achieve the desired position for each bundle. The graft was placed in the fork of the positioning tool with one bundle on either side of the fork. The single strand of the suture over which the graft was looped was passed through the femoral tunnel until it was out of the lateral thigh, and this suture was used to pull the graft into the tunnel. The graft-positioning tool was advanced through the tibial tunnel until it reached the aperture of the femoral tunnel. At this point, the AM and PL bundles were rotated by rotating the positioning tool to achieve their desired positions before they were advanced into the femoral tunnel (Fig. 3D, E). A femoral INTRAFIX screw (DePuy Mitek) was driven between the strands to separate the two bundles within the single tunnel. For the tibial tunnel fixation, the two bundles were placed in opposite quadrants of the sheath at their anatomical insertion sites on the tibial plateau using the tibial INTRAFIX system (DePuy Mitek). While the graft was secured, 40 N of graft tension were applied by an interference screw at full extension. Illustrative surgical diagrams are presented in Fig. 4.

Fig. 3figure 3

Surgical procedures for STDB ACL reconstruction under arthroscopy. A Diagnosis of ACL rupture under arthroscopy. B Femoral tunnel. C Tibial tunnel. D Grafts were pulled into the femoral tunnel. E Reconstructed ACL

Fig. 4figure 4

Illustrative surgical diagrams for STDB ACL reconstruction. A Femoral insertion in medial surface of the lateral femur condyle. B Tibial insertions (AM tunnel and PL tunnel) into the tibial plateau. ANT anterior, DIST distal, LAT lateral, MED medial, POST posterior, PROX proximal

Postoperative treatment and rehabilitation

Cefoxitin 1 g bid was administered during the first 48 h postoperatively to prevent infection in all the patients. The affected limb was wrapped in cotton pad for 72 h. Three-dimensional computed tomography (3D CT) was performed immediately after surgery to evaluate the bone tunnel and fixation, and MRI was applied to check the ligament healing at the last postsurgical follow-up.

The same postoperative rehabilitation plan was executed in both groups. The affected limb was immobilized with adjustable support. The patients were allowed to walk with crutches while being protected properly by knee braces on the second day after surgery. They were encouraged to flex their knees from 0 to 90° within 2–4 weeks and further to 120° within 6–8 weeks. However, they were instructed not to flex the knee over 120° in the first 3 months postoperatively. The braces were worn for at least 2 months. The patients were allowed to swim and ride a bicycle 6 months after surgery, begin jogging 10 months after surgery, and participate in strenuous exercises 18 months after surgery [16].

Outcome measures

Clinical outcome was assessed based on the International Knee Documentation Committee (IKDC), Lysholm, and Tegner scores and physical examinations performed both before surgery and at the last follow-up for all the patients.

Statistical analysis

Data were expressed as the mean ± standard deviation (SD) and analyzed by SPSS 18.0 software (SPSS Inc., Chicago, IL, USA). The independent-samples t-test and χ2 test were performed on the general data from the patients. Preoperative and postoperative IKDC, Lysholm, and Tegner scores and KT-3000 measurements were tested for Mann–Whitney U rank. Fisher’s exact test was used for the Lachman test and pivot shift test. P  < 0.05 was considered statistically significant.

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